r = sqrt(A2(5, 5)^2 + A2(12, 5)^2);
c = A2(5, 5) / r; s = A2(12, 5) / r;
G = eye(13);
G(5, 5) = c; G(5, 12) = s; G(12, 5) = -s; G(12, 12) = c;
G3 = G;
A3 = G * A2;